The invention relates to a method of measuring acceleration and vibration using a fibre-optic sensor and to a device or arrangement measuring acceleration and vibration having a light source, an optical fibre, a reflector and a photodetector.
Measuring methods and measuring devices of such a type are described in literature as vibration and range sensors.
In one construction, a variation in the distance between a transmitting and a receiving fibre and a reflective surface is measured by means of the corresponding variation in intensity. Here, multi-mode fibres are used as optical fibres. Although, on account of the multi-mode fibre technology used, said sensors are relatively easy to realize, because of their open design principle they may be used only in a relatively protected environment with short glass-fibre transmission links. It is not possible to realize long transmission links because of the extensive damping in the multi-mode fibre. Such sensors are sold, for example, by the company TETRA Gesellschaft fur Sensorik, Robotik und Automation mbH, llmenau, Germany.
From EP 0 456 681 B1, a fibre-optic accelerometer based on a Fabry-Perot interferometer is known, in which a diaphragm deformable by acceleration is provided. Fastened in the centre of the diaphragm is a hemispherical mirror, opposite which lies the end of an optical fibre. Upon deformation of the diaphragm, the variation in the distance between fibre end and mirror is measured by interferometry according to the Fabry-Perot principle and used to calculate the acceleration. The drawback is that such a diaphragm is sensitive and costly to clamp and hold.
From DE 3 939 573 A1 a device is known, in which a clamped fibre is immersed into a flowing environment. Said flowing environment bends the end of the optical fibre out of its position of rest and hence alters the distance from a position detector which responds to light intensity. A similarly operating device is known from U.S. Pat. No. 3,602 037, in which a light-guiding rod is bent under the influence of forces, thereby reducing the dimension of the light beams which exit at its end and are picked up by a photodetector. Such constructions are however unsuitable for high-precision vibration and acceleration measurements, especially as such equipment is of a relatively large size.